This invention relates to blitting.
Multimedia programs and games often display animation on a computer screen using "sprites". Sprites are "blitted" (short for "block transferred") onto a background scene in a rapid sequence to create the illusion of motion. Blitting must be performed many times per second to create smooth animation. On occasion, many animation sequences are run simultaneously, which increases the computational load on the computer.
A first common method of performing blitting is to examine each pixel in the stored sprite and determine whether the pixel has the code for a transparent color. If not, the pixel is opaque, and is copied onto the background.
A second common approach is to create and save a sprite with white pixels in place of the transparent pixels along with a "mask" bitmap. The mask contains white pixels in place of transparent pixels, and black pixels in place of opaque pixels. When the sprite is to be displayed, the mask is ANDed with the background to create a resulting image with black pixels where the sprite will be located. This resulting image is then ORed with the sprite, to insert the sprite at the black pixels.
In addition to the above methods used in general purpose computers, some special purpose game machines, such as Sega.RTM. and Nintendo.RTM., contain hardware to perform blitting very quickly.